Translatable carriage fixation system

ABSTRACT

Translational bone fixation assemblies, kits containing such assemblies, and methods of use are described herein. The described assemblies may be used in spinal fusion procedures in which a damaged or diseased disc (or part of a disc) is removed from between a pair of vertebrae and a spinal fusion spacer is placed between the vertebrae. The assemblies may be applied to an anterior portion of the affected vertebrae to span the affected disc space, and may be fixed to the vertebrae using bone screws. The assemblies may function to maintain the vertebrae aligned during the initial period following fixation in which fusion of the spacer to the adjacent vertebrae occurs. The assemblies may also function to share some of the axial spinal load applied to the fusion spacer to prevent extreme subsidence of the spacer into the vertebral body, such as where the patient has poor bone quality.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 11/217,959, filed Aug. 31, 2005 now U.S. Pat. No. 7,666,185, whichis a continuation-in-part of U.S. patent application Ser. No.10/932,392, filed Sep. 2, 2004 now abandoned, which is acontinuation-in-part of U.S. patent application Ser. No. 10/653,164,filed Sep. 3, 2003 now U.S. Pat. No. 7,857,839, the entire disclosure ofeach application is expressly incorporated by reference herein.

FIELD OF THE INVENTION

The present invention is related to a fixation system. Moreparticularly, the invention is related to a fixation system consistingof a translational plate system with a plurality of fixation holes.

BACKGROUND OF THE INVENTION

Orthopedic fixation devices such as plates are frequently coupled tobone with fasteners inserted through plate holes. It is known thatsecuring such fasteners to the bone plate, for example through the useof expansion-head screws, can decrease the incidence of loosening of thefixation assembly post-operatively. It is also known that a bushing maybe disposed in each plate hole to receive the fastener to permitpolyaxial movement so that the fastener may be angulated at asurgeon-selected angle. However, polyaxial movement of fasteners throughset plate hole locations only increases attachment alternatives of thefasteners themselves. The plate holes remain fixed in relation to eachother and to the longitudinal axis of the plate.

Typically, a spinal fixation plate is applied to the anterior side ofthe affected vertebrae to span at least one affected disc space orvertebra (i.e. one in which at least a portion of the disc has beenremoved and a spinal fusion spacer has been inserted). The plate isfixed to the vertebrae using bone screws and acts to keep the vertebraegenerally aligned during the initial period following fixation in whichfusion of the spacer to the adjacent vertebrae occurs. The plate alsomay act to prevent the spacer from being expelled from the disc spaceduring this initial period.

Where a spinal fusion spacer is implanted between a pair of vertebrae tobe fused, the spacer rests on the endplates of the vertebrae. The outercircumference of the end plates comprises hard cortical bone and thusprovides the best surface upon which to seat the spacer. The centerportion of the endplates comprises a thin cortical bone shell overlyinga core of softer cancellous bone. Most, if not all, of the spacercontact surface, however, may be located in this center portion.

Subsequent to placement of the spacer, the surgeon typically compressesthe disc space by pressing the adjacent vertebrae together. Thiscompression ensures a good engagement between the spacer and theendplates, increasing the chances that fusion will occur. Often in theperiod immediately following surgery, the spacer may subside slightlyinto the under-portion of the endplates, or the space between thevertebral endplates may decrease due to graft resorption (in the case ofallograft spacers).

Where a rigid fixation plate is used to connect the vertebrae, thissubsidence may tend to shift more of the spinal load to the plate thanis desirable. Such load shifting can also occur due to inaccuracies ininstalling the plate to the vertebrae. In extreme circumstances, thisload shifting can result in non-fusion of the spacer to the vertebra,since firm compression between the spacer and the vertebrae is onefactor contributing to successful fusion.

Accordingly, there exists a need for a fixation system which providesthe desired support to the vertebrae to be fused, and which allowslimited translation of the vertebrae with respect to at least a portionof the plate, thereby limiting the undesirable effects of load shieldingby the plate due to graft subsidence caused by settling or normal forcesexperienced in the spinal column. Promoting fusion of the adjacentvertebrae may thus accomplished.

Translation plates which compensate for this subsidence by providing theaforementioned benefits of a rigid fixation plate (general vertebralalignment, and prevention of spacer expulsion), while allowing at leastone vertebra to move with respect to the plate to compensate forpost-surgical subsidence, may be desirable. This compensation may permitthe majority of the spinal column load to be borne by the spacer ratherthan the plate.

SUMMARY OF THE INVENTION

An embodiment of a bone fixation assembly is described, comprising: afirst plate having a first end, a second end, a longitudinal axis, andupper surface, and a lower surface, the first plate having at least twofixation holes extending from the upper surface to the lower surface,the first plate further comprising first and second extending segmentsextending near the first end of the first plate in the direction of thelongitudinal axis, the first extending segment associated with the uppersurface and the second extending segment associated with the lowersurface, and a first cavity formed between the extending segments; andat least one carriage block having at least two fixation holes; whereinthe at least one carriage block is received and retained within thefirst cavity and is slidably moveable with respect to the first plate.

The first plate may further comprise a second cavity. The assembly mayfurther comprise a second carriage block slidably associated with thefirst plate within the second cavity. The second carriage block may beslidable independent of the first carriage block. The second carriageblock may comprise at least two fixation holes.

The first and second carriage blocks may be permitted to slidesimultaneously. The first carriage block may be permitted to slide overa greater distance than that of the second carriage block. The slidingdistance of the second carriage block may be limited by amotion-limiting element. The first carriage block may be permitted toslide from about 0 mm to about 10 mm relative to the first plate.

The first plate may further comprise at least one recess. The assemblymay further comprise a securing element insertable in a recess. Thesecuring element may be able to limit the translatable movement of thefirst carriage block along the longitudinal axis. At least one recessmay extend from the upper surface to the lower surface. At least onerecess may be substantially circular, substantially oblong, and/orsubstantially polygonal. At least one recess may be able to receive adrill guide, and/or a temporary attachment element.

The first plate may have four fixation holes, and wherein the fixationholes are arranged in pairs. The first plate further may comprise atleast one indent able to facilitate the bending of the first plate. Atleast two fixation holes may be substantially circular, and may furthercomprise a clip. At least two fixation holes may be substantiallyoblong. At least two fixation holes may each have a longitudinal axis,and wherein the at least two fixation holes allow for the translation ofa fastener along the longitudinal axis of each of the at least twofixation holes. At least two fixation holes may allow for selectiveplacement of a fastener within each of the at least two fixation holes.

The first plate further may comprise at least one internal fixationelement slidably associated with the first plate. At least one internalfixation element may further comprises at least one fixation hole. Atleast one internal fixation element may be slidably translatable inrelation to the fixation holes of the first plate. At least one internalfixation element may also be slidably translatable in relation to thefixation holes of the first carriage block. The first plate may furthercomprise a groove, and wherein at least one internal fixation element isable to situated in the groove.

The first carriage block may experience a frictional force of at least50 grams when slidably moving in relation to the first plate.

The first and second extending segments may each have a longitudinalaxis, and wherein the longitudinal axes of the first and secondextending segments are divergent. The first and second extendingsegments may also each have a longitudinal axis, and wherein thelongitudinal axes of the first and second extending segments areconvergent. Further, the first and second extending segments may eachhave a longitudinal axis, and wherein the longitudinal axes of the firstand second extending segments are substantially parallel.

The first plate may comprise a length, and wherein the length of thefirst plate is from about 10 mm to about 140 mm. The first carriageblock may comprise a length, and wherein the length of the firstcarriage block is from about 5 mm to about 20 mm.

Another embodiment of a translational bone fixation assembly isdescribed, comprising: a first plate having a plurality of fixationholes and a longitudinal axis; and at least a first carriage blockhaving a plurality of fixation holes, at least a portion of the firstcarriage block slidably associated with at least a portion of the firstplate; wherein the first carriage block is translatable in the directionof the longitudinal axis when the assembly is attached to at least onebone segment.

The assembly may further comprise a second carriage block slidablyassociated with at least a portion of the first plate. The secondcarriage block may be slidable independent of the first carriage block.The second carriage block may comprise a plurality of fixation holes.

The first and second carriage blocks may be permitted to slidesimultaneously. The first carriage block may have a range of motiongreater than that of the second carriage block. The range of motion ofthe second carriage block may be limited by a motion-limiting element.The first carriage block may be permitted to slide from about 0 mm toabout 4 mm relative to the first plate.

The first plate further may comprise a bore, and wherein an extensionelement extends through the bore. The extension element may be able tostop the sliding movement of the first carriage block. The extensionelement may be permanently attached to the first plate.

Another embodiment of a translational bone fixation assembly isdescribed, comprising: a first plate having a plurality of fixationholes and a longitudinal axis; and at least a first carriage blockhaving a plurality of fixation holes, at least a portion of the firstcarriage block slidably associated with at least a portion of the firstplate; wherein the first carriage block is translatable in the directionof the longitudinal axis under a coaxial force of at least about 50grams.

The assembly may further comprise a second carriage block slidablyassociated with at least a portion of the first plate. The secondcarriage block may be slidable independent of the first carriage block.The second carriage block may comprise a plurality of fixation holes.

The first and second carriage blocks may be permitted to slidesimultaneously. The first carriage block may have a range of motiongreater than that of the second carriage block. The range of motion ofthe second carriage block may be limited by a motion-limiting element.The first carriage block may be permitted to slide from about 0 mm toabout 10 mm relative to the first plate.

A method of securing at least two bone elements is described, comprisingthe steps of: (a) providing a translatable bone fixation assembly havinga first plate having a plurality of fixation holes and a longitudinalaxis, and a first carriage block having a plurality of fixation holes,wherein the carriage block is slidably associated with the first plate;(b) inserting at least one fastener through at least one fixation holein the first plate and into a first bone element; (c) inserting at leastone fastener through at least one fixation hole in the first carriageblock and into a second bone element; and (d) permitting the carriageblock to slide in the direction of the longitudinal axis afterimplantation of the bone fixation assembly.

The assembly may further comprise a second carriage block slidablyassociated with the first plate, and wherein the second carriage blockhas a plurality of fixation holes. The method may further comprise thestep, inserted before step (d), of inserting at least one fastenerthrough at least one fixation hole in the second carriage block and intoa third bone element.

The third and second bone elements may be separated by the first boneelement.

The method may further comprise the step of inserting applying amotion-limiting element to limit the motion of the first carriage block.The method may further comprise the step, inserted before step (b), ofdrilling at least one hole in at least one bone element in a location ofdesired fastener insertion.

The first and second bone elements may be adjacent vertebrae.

The method may further comprise the step of inserting an intervertebralspacer between the first and second bone elements.

A kit for use with bone fixation procedures is also described,comprising: at least a first plate having a plurality of fixation holesand a longitudinal axis; at least a first carriage block having aplurality of fixation holes, at least a portion of the first carriageblock slidably associated with at least a portion of a first plate;wherein the first carriage block is translatable in the direction of thelongitudinal axis when the assembly is attached to at least one bonesegment.

The kit may further comprise at a first fastener for use with at leastone fixation hole. The kit may further comprise a second fastener foruse with at least one fixation hole, wherein the first fastener issubstantially different than the second fastener.

The kit may further comprise a second plate and a second carriage block.The first carriage block may be slidably associated with the secondplate. The second carriage block may be slidably associated with thefirst plate. The first and second carriage blocks may be able to besimultaneously slidably associated with the first plate.

The kit may further comprise at least one motion-limiting element foruse with a carriage block. The kit may further comprise at least onetemporary attachment element. The kit may further comprising at leastone drill guide, and/or at least one drill.

At least a portion of the first plate slidingly engaged with the firstcarriage block is a dovetail portion, wherein at least a portion of thedovetail may be deformed to limit the translational motion of the firstcarriage block.

BRIEF DESCRIPTION OF THE DRAWINGS

While preferred features of the present invention may be disclosed inthe accompanying illustrative, exemplary drawings, for the purposes ofdescription, the invention as defined by the claims should be in no waylimited to such preferred features or illustrative and exemplarydrawings, wherein:

FIG. 1 a is a perspective view of an embodiment of a translationalspinal plate in a fully compressed configuration;

FIG. 1 b is a perspective view of the plate of FIG. 1 a in a fullyextended configuration;

FIG. 1 c is a cross-sectional view of the plate of FIG. 1 b, taken alongline A-A;

FIG. 1 d is an enlarged partial cross-sectional view of the plate ofFIG. 1 b taken along the line A-A;

FIG. 1 e is a partial elevation view of the plate of FIG. 1 b, takenalong line B-B;

FIG. 1 f is a top view of an embodiment of the carriage block of FIG. 1a;

FIG. 1 g is a front view of the carriage block of FIG. 1 f;

FIG. 2 a is a side view of an exemplary bone fastener for use with theplate of FIG. 1 a;

FIG. 2 b is a top view of an exemplary retention clip for use with theplate of FIG. 1 a;

FIG. 3 a is a perspective view of an embodiment of a translating spinalplate for use in a two-level spinal fusion procedure, the plate beingshown in the fully extended position;

FIG. 3 b is a perspective view of the plate of FIG. 3 a, in the fullycompressed condition;

FIG. 3 c is a partial top view of the plate of FIG. 3 a;

FIG. 3 d is a partial top view of a hexagon-shaped recess for use with aplate;

FIG. 3 e is an partial top view of a square-shaped recess for use with aplate;

FIG. 3 f is a top view of an embodiment of a translational spinal platewith an overlapping hexagonal recess;

FIG. 4 a is a top view of another embodiment of a translational spinalplate with a pair of slotted bone screw holes;

FIG. 4 b is a top view of the slotted bone screw hole of FIG. 4 a;

FIG. 5 a is a perspective view of another embodiment of a translationalspinal plate with an internal carriage block;

FIG. 5 b is a cross-sectional view of the plate of FIG. 5 a taken alongthe line F-F;

FIG. 5 c is a perspective view of a two-piece internal carriage blockthat may be used with the plate of FIG. 5 a;

FIG. 6 is perspective view of another embodiment of a translationalspinal plate with a plurality of internal carriage blocks;

FIG. 7 a is a top view of another embodiment of a translational spinalplate with both a pair of slotted bone screw holes and an internalcarriage block;

FIG. 7 b is perspective view of another embodiment of a four-leveltranslational spinal plate with two pairs of slotted holes;

FIG. 7 c is a top view of the plate of FIG. 7 b;

FIG. 8 a is an exploded view of another embodiment of a translationalspinal plate with a two-piece track-plate construction;

FIG. 8 b is a top view of the plate of FIG. 8 a in an assembledcondition;

FIG. 8 c is a front view of an embodiment of a symmetrical carriageblock;

FIG. 8 d is a top view of the carriage block of FIG. 8 c;

FIG. 8 e is a front view of an embodiment of an offset carriage block;

FIG. 8 f is a top view of the carriage block of FIG. 8 e;

FIG. 8 g is a top view of an alternative carriage block design for usewith the track-plate of FIG. 8 a;

FIG. 9 is a top view of a motion-limiting shim;

FIG. 10 is a top view of another embodiment of a translational spinalplate, this embodiment having a cam-compression feature;

FIG. 11 is a perspective view of a corpectomy model of a translationalspinal plate;

FIG. 12 a is a top view of a further embodiment of an extensibletranslational spinal plate in a compressed position;

FIG. 12 b is a top view of the plate of FIG. 12 a in an extendedposition;

FIG. 13 a is a perspective view of another embodiment of a translationalspinal plate having a dovetail design;

FIG. 13 b is a cross-sectional view of the plate of FIG. 13 a takenalong the line G-G;

FIG. 14 a is a perspective view of yet another embodiment of atranslational spinal plate having a dovetail design in a compressedcondition;

FIG. 14 b is a perspective view of the plate of FIG. 14 a in an expandedcondition;

FIG. 15 is a perspective view of the base plate of FIGS. 14 a-14 b, witha carriage block removed for clarity;

FIG. 16 is a perspective view of a carriage block for use with the plateof FIG. 15;

FIG. 17 a is a perspective view of still another embodiment of atranslational spinal plate having a dovetail design in a expandedcondition; and

FIG. 17 b is a perspective view of the plate of FIG. 17 a in a partiallycompressed condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The plates described herein may be used in spinal fusion procedures inwhich a damaged or diseased disc (or part of a disc) is removed frombetween a pair of vertebrae and a spinal fusion spacer is placed betweenthe vertebrae. The plates may be applied to an anterior portion of theaffected vertebrae to span the affected disc space, and may be fixed tothe vertebrae using bone screws. The plate may function to maintain thevertebrae aligned during the initial period following fixation in whichfusion of the spacer to the adjacent vertebrae occurs. The plate mayalso function to share some of the axial spinal load applied to thefusion spacer to prevent extreme subsidence of the spacer into thevertebral body, such as where the patient has poor bone quality. Theplates may also act to prevent the spacer from being expelled from thedisc space during the initial post-operative period.

The plates may be used for single level (i.e. one-disc) ormultiple-level (i.e. multiple disc) fusion procedures. Some embodimentsmay be used for corpectomy procedures, in which at least a portion of avertebral body is removed. Single level plates generally may have twopairs of bone screw holes, while the multi-level plates generally mayhave three or more pairs of holes. While the plates herein are describedwith reference and application to the spine, it will be appreciated thatfeatures of the plates and the plates may have other applications, andcan be applied to other bones and/or parts of the skeleton.

FIG. 1 a shows a translating spinal fixation plate 1 for use in asingle-level fusion procedure in which first plate segment 2 andcarriage block 4 are configured to be fixed to first and second vertebraso that the plate 1 spans the disc space between the vertebrae. Theplate 1 may have a longitudinal axis A-A and the first plate segment 2and carriage block 4 may each have one or more bone fastener hole(s) 6,8 for receiving a bone fastener 40 to fix the respective plate segmentand carriage block to the associated vertebral body. The first platesegment 2 may have upper and lower surfaces 10, 12, while carriage block4 may have upper and lower surfaces 14, 16. The lower surfaces 12, 16may be configured to engage a portion of a respective vertebral body. Inthe illustrated embodiment, the first plate segment 2 and carriage block4 are configured to be fixed to the anterior surfaces of a pair ofadjacent vertebra. FIG. 1 f shows a top view of the carriage block 4 inmore detail, and FIG. 1 g shows a front view of the same.

As illustrated in FIGS. 1 b-1 e, the first plate segment 2 may haverespective translating surfaces 18 a, 18 b, while the carriage block 4may have respective translating surfaces 20 a, 20 b configured to allowthe segment and carriage block to slide toward (or away from) eachanother along the longitudinal axis A-A of the plate 1. The plate 1 mayhave an initial length “PL_(E)” sufficient to span the disc space and toallow fixation of a plate segment 2 and carriage block 4 to eachvertebra.

The translating surfaces are illustrated in more detail in FIGS. 1 c-1e, in which the respective translating surfaces are configured anddimensioned to cooperate to allow the first plate segment 2 and carriageblock 4 to slide with respect to each other, while maintaining thedesired structural integrity of the plate 1 in bending and torsion.Thus, when the first plate segment 2 and carriage block 4 are fixed torespective adjacent vertebrae using bone fasteners, subsequent movementof the vertebrae along the axis of the spine (e.g. due to subsidence ofthe intervertebral spacer into the end plates of the associatedvertebral bodies) may cause the first plate segment 2 and carriage block4 to slide together along the longitudinal axis A-A, reducing the length“PL_(C)” of the plate 1. Preferably the plate segment 2 and the carriageblock 4 will move in an amount equal to the amount of subsidence of thespacer into the adjacent vertebrae.

The translation of the carriage block 4 with respect to the first platesegment 2 is contemplated and preferably provided by spinal fixationplate 1 after it has been implanted into the body. Such translation maybe urged by, for example, forces within the spinal column that maydirectly bear upon fasteners inserted into fastener holes 6, 8 of firstplate segment 2 and carriage block 4. When a translating force acts insitu upon the first plate segment 2 and/or the carriage block 4,translating surface 20 a may translate relative to translating surface18 a, or vice versa. Likewise, translating surface 18 b may translaterelative to translating surface 20 b, or vice versa. As described inmore detail below, the respective pairs of translating surfaces 18 a, 20a and 18 b, 20 b may or may not contact each other during thetranslation of the carriage block 4 relative to the first plate segment2. Moreover, any of all of translating surfaces 18 a, 18 b, 20 a, 20 bmay be angled, or for example, roughened, to produce a desired contactand/or resistance to translation between the respective pairs oftranslating surfaces 18 a, 20 a and 18 b, 20 b. Such variations are alsodescribed in more detail below.

The first plate segment 2 and carriage block 4 may also have respectivecompression stop surfaces 22 a, 22 b; 24 a, 24 b that may engage eachother when the plate is in the fully compressed condition (see FIG. 1a). The first plate segment 2 and carriage block 4 may further haverespective extension stop surfaces, 27 a, 28 (see FIG. 1 e) that mayengage each other when the plate is in the fully extended condition (seeFIG. 1 b). The first extension stop surface 27 a may take the form of anextension member 27, such as, for example, a rivet, pin, screw or othersuitable extension disposed in a bore 30 in the first plate segment 2.The second extension stop surface 28 may comprise an end surface of thesecond plate segment 4. The second extension stop surface 28 may atleast partially conform to the shape of the first extension stop surface27 a. The extension member 27 may be removably attached to the firstplate segment 2 to allow substitution of different-sized or differentstyled carriage blocks 4 may be permanently fixed to the first plateassembly to capture the carriage block 4 and prevent disassembly. Whenthe plate 1 is assembled, the first plate segment 2 and carriage block 4may slide between the fully extended and fully compressed conditions,the amount of compression (or extension) of the plate may be limited bythe arrangement of the stop surfaces. It will be recognized that theplate 1, and particularly the first plate segment 2 and the carriageblock 4 may employ other stop surfaces to limit the amount of travel ofthe carriage block 4 with response to the first plate segment 2.

The plate segments and carriage blocks may each have a first width “PW1”corresponding to the dimension transverse to the longitudinal axis asmeasured across the portion of the plate having the bone fastener holes6 a, 6 b, 8 a, 8 b. The first plate segment 2 and carriage block 4further may have a second width “PW2” as measured across the portion ofthe respective segment that does not contain the bone fastener holes.The first width PW1 may be about 10 mm to about 60 mm, while the secondwidth PW2 may be about 6 mm to about 56 mm. The first plate segment 2and carriage block 4 may have specialized widths for spinalapplications. For example, for assemblies used in the cervical region,PW1 may be from about 10 mm to about 20 mm and PW2 may be from about 6mm to about 20 mm. Also, for assemblies used in the thorcolumbar region,PW1 may be from about 16 mm to about 30 mm and PW2 may be from about 10mm to about 30 mm. Further, for assemblies used in the lumbar region,PW1 may be from about 20 mm to about 60 mm and PW2 may be from about 16mm to about 60 mm. The first plate segment 2 and carriage block 4 mayeach have a thickness “PT” which may be about 1 mm to about 10 mm, andmore preferably from about 2 mm to about 4 mm.

In the fully compressed condition, the plate length PL may be from about10 mm to about 138 mm, and in the fully extended condition the platelength PL may be from about 12 mm to about 140 mm. The compressed andextended lengths may vary depending on the size of the patient, theregion of the spine in which the plate is used. Thus, larger sizes maybe used for lumbar spine applications in larger patients, while smallersizes may be used for cervical spine applications in small patients.

The plate 1 may be curved to more naturally conform the plate to thenormal anatomical curvature of the spinal column. Thus, when used in thecervical and lumbar spine, the plate may have a lordosed, or convexshape. When used in the thoracic spine, the plate may have a kyphosed,or concave shape. Alternatively, the plate may be provided in a flatconfiguration to fit to a lateral portion of the spine. The first platesegment 2 and carriage block 4, and in particular their lower surface12, 16, may also be provided with a lateral curvature allowing them toclosely conform to individual vertebral elements. For example, as seenin FIGS. 1 c-1 g, carriage block 4 may have a radius R_(C) along itslower surface 16, and the first plate segment 2 may have a radius R_(P)along its lower surface 12. Radius R_(C) may be from about 10 mm toabout 60 mm, and radius R_(P) may be from about 10 mm to about 60 mm.The first plate segment 2 and carriage block 4 may also be bendable toallow the surgeon to modify the plate curvature as desired to customizethe plate to the anatomy of an individual patient.

The lower surfaces 12, 16 of the first plate segment 2 and carriageblock 4 may be roughened to enhance engagement between the plate and theassociated vertebral body. Such roughening may be achieved by beadblasting the surfaces 12, 16 by machining ridges, grooves, or othersurface profiles or projections into the surfaces, or by applying aroughening material to the lower surfaces.

FIGS. 1 c-1 e illustrate translating surfaces 18, 20 of plate 1configured to provide a compression-resisting force that varies with theamount of translation between the first plate segment 2 and carriageblock 4. As shown, the first plate segment 2 has upper and lowerextending segments 33 a, 33 b each having a translating surface 18 a, 18b configured to slidably engage the surfaces 20 a, 20 b of the carriageblock 4. As shown in FIG. 1 e, the translating surfaces 18 a, 18 b ofthe first plate segment 2 may form an angle α with respect to each otherso that as the carriage block 4 moves, the carriage block 4 wedgesagainst the translating surfaces 18 a, 18 b of the first plate segment 2thus providing a force that increasingly opposes movement of thecarriage block 4 as the carriage block 4 travels toward the vertex ofangle α. In the embodiment shown in FIG. 1 e, angle α is slightlydivergent. Alternatively, however, angle α may be convergent, such thatsurfaces 18 a, 18 b of the carriage block 4 may encounter more frictionas carriage block 4 translates toward the first and second ends 32 a, 32b of the first and second extending segments 33 a, 33 b of first platesegment 2. Moreover, angle α may not exist at all if surfaces 18 a, 18 bare substantially parallel. This may be preferable in light of thefitting and contouring options discussed below. All of these designs maybe useful in preventing extreme subsidence of the associatedintervertebral spacer. The wedge angle α may be from about 1 degrees toabout 10 degrees, and may generally correspond to variances in therecess height RH along the longitudinal axis of the first plate segment2. Moreover, the translating surfaces of the first plate segment 2 andcarriage block 4 surfaces may be provided with ratchet teeth, grooves,roughened portions, or other surface features to provide the desiredincreased resistance to compression. Further, the carriage block 4 maybe slightly oversized in relation to the sliding area provided by thefirst plate segment 2, so as to create a frictional fit, but stillallowing translation of the carriage block 4 while engaging the firstplate segment 2.

As further shown in FIG. 1 e, upper and lower surfaces 10, 12 of thefirst plate segment 2 may also form an angle β with respect to eachother. Angle β may be substantially the same as wedge angle α, discussedabove. As with angle α, angle β may be convergent, divergent, or notexist at all if upper and lower surfaces 10, 12 are substantiallyparallel. It is contemplated that any combination of suitable angles αand β may be formed on a single plate segment, such as first platesegment 2. Moreover, angle β may generally correspond to variances inthe plate thickness PT along the longitudinal axis of the first platesegment 2.

The wedge angle α may be formed with a variety of arrangements and/ortechniques. First, the translating surfaces 18 a, 18 b and/or 20 a, 20 bcould be machined to create the wedge angle α. Alternatively, thesegments 33 a, 33 b could be bent and held at a certain distance thatwould create the wedge angle α, which would create the desiredfrictional fit between the carriage block 4 and the first plate segment2 to achieve the desired control of movement between the carriage block4 and the first plate segment 2 after implantation into the body. Apreferred exemplary plate may require about 50 grams to about 1600 gramsof force to move the carriage block 4 relative to the first platesegment. More specifically, an exemplary, illustrative plate forcervical applications may require about 50 grams to about 400 grams, andmore preferably about 180 to about 220 grams. An exemplary, illustrativeplate for lumbar and thorcolumbar applications may require about 100grams to about 1600 grams, and more preferably about 400 grams to about800 grams. The first plate segment 2 and carriage block 4 may also bedesigned so that the carriage block moves relatively freely with littleor no friction.

FIG. 1 e also shows relevant distances of the translating first platesegment 2 and carriage block 4. As viewed from the side, the translatingupper and lower surfaces 18 a, 18 b, and side surface 18 c of the firstplate segment 2 may form a cavity 15 within the first plate segment 2.The cavity 15 has a total length “RL”, and a recess height “RH”. Asviewed from the side, the carriage block 4 has a total length “BL” whichextends, in this embodiment, from stop surface 24 b to carriage blockend 39. Carriage block also has an translating carriage height “CH”. Theportion of the recess engaging the carriage block 4 is defined by lengthRL₂, while the remaining portion of the recess left void has a lengthRL₁. It is seen that carriage block 4 has a side surface 20 c from thisperspective. The portion of the carriage block 4 that extends outwardlyfrom the side surface 20 c to the stop surface 24 b has a length BL₁.The portion of the carriage block 4 has extends inwardly from the sidesurface 20 c to the first extension stop surface 27 a has a length BL₂.The remainder of the carriage block 4 has a length BL₃. Therefore, thetranslating relationship between the carriage block 4 and first platesegment 2 can be described as follows: as carriage block 4 slides intocavity 15 of first plate segment 2, BL₂ and RL₂ may increase, and BL₃and RL₁ may consequently decrease. The aforementioned distances may bearany relationship that is suitable for creating the desired spatialrelationship of the first plate segment 2 and carriage block 4, and thedimensional preferences of the components therein.

FIGS. 1 f-1 g show a carriage block 4 in more detail. FIG. 1 f shows acarriage block from a top view, while FIG. 1 g shows a carriage block 4from a front view. Lengths BL, BL₁, BL₂, and BL₃ are shown, and maycorrespond to the discussion above in reference to FIG. 1 e. Likewise,the translating height CH of carriage block 4 is shown, and maysimilarly correspond to the discussion above in reference to FIG. 1 e.Carriage block 4 may have two ends 39 a, 39 b near fastener holes 6 a, 6b. Carriage block 4 also may have ridges 29 a, 29 b along the uppersurface 14. Ridges 29 a, 29 b may partially define the boundaries of thetranslating surface 20 a of the carriage block 4, and may vary in widthalong the longitudinal axis H-H of carriage block 4. Specifically,ridges 29 a, 29 b may span a first width RW₁ and a second width RW₂.First width RW₁ may generally correspond to the upper surface 10 offirst plate segment 2 near the stop surfaces 24 a, 24 b (see, e.g.,FIGS. 1 a-1 b). Second width RW₂ may generally correspond to thedimensions of the first plate segment 2 near its extending segments 33a, 33 b (see, e.g., FIG. 1 e).

Ridges 29 a, 29 b may also form angled portions 20 d of the uppertranslating surface 20 a. Such angled portions 20 d may be utilized toengage an upper extending segment 33 a of a first plate segment 2 duringtranslation. The configuration of the respective translating surfaces 18a, 20 a, and 20 d thus may operate to retain the carriage block 4 inclose engagement with the first plate segment 2, facilitating movementof the block 4 along the longitudinal axis A-A as previously described.It is contemplated, however, that other features may be used to gain thebenefits of ridges 29 a, 29 b and angled portions 20 d, such as grooves,notches, teeth, or other suitable retention or alignment designs.

Carriage block 4 may also have a curved surface 39 c between ends 39 a,39 b, and curved surface 39 c may include second extension stop surface28. In use, curved surface 39 c and second extension stop surface 28 mayengage the side surfaces 27 a, 27 b of an extension member 27. When theplate 1 is in its compressed state, as shown in FIG. 1 a, the extensionmember 27 may be adjacent to second extension stop surface 28. Adetailed view of this arrangement is also shown in FIG. 1 e, discussedsupra, wherein first extension stop surface 27 a abuts second extensionstop surface 28. As carriage block 4 translates from the compressedposition, curved surface 39 c may engage the side surfaces of extensionmember 27. The relationship between curved surface 39 c and extensionmember 27 is also shown in FIG. 1 c.

FIG. 1 c also shows an exemplary fastener screw hole 6 a, 6 b configuredto receive a retention clip 38 to engage an associated bone fastener 40to prevent back-out of the fastener during use. Clip 38 (see FIG. 2 b)resides at least partially within a circumferential groove 42 in thebone fastener hole 6 a, 6 b, so that a portion of the clip 38 protrudesinto the bone fastener hole 6 a, 6 b. The clip 38 is configured toengage a circumferential groove 44 in the head 46 of the bone fastener40 (see FIG. 2 a) when the fastener is placed in the hole 6 a, 6 b anddriven into the underlying bone. It should be noted that fastener holes8 a, 8 b may exhibit all or some of the same characteristics as fastenerholes 6 a, 6 b.

FIG. 2 b shows an exemplary retention clip 38 having a generallywishbone shape. The clip 38 may have generally parallel arms 48, 50 anda connecting portion 52 that may permit elastic expansion/compression ofthe arms that allow the clip arms 48, 50 to expand when the bonefastener 40 is inserted, and to contract when the clip 38 engages thegroove 44 in the fastener head 40. The clip may have a length “CL” Theclip 38 may further have an aligning projection 54 that extends fromconnecting portion 52 in a direction opposite that of the arms 48, 50.The aligning projection 54 may be received within a corresponding recess(not shown) in the plate 1 to maintain the clip 38 in a desiredorientation with respect to the plate 1. While carriage block 4 has beenillustrated and described as having a pair of bone fastener holes 6 a, 6b, carriage block 4 may have a single bone fastener hole, three bonefastener holes (as shown in FIG. 8 g, discussed infra), or any number ofbone fastener holes. Likewise, while first bone plate segment 2 has beenillustrated and described with a pair of bone fastener holes 8 a, 8 b,first bone plate segment 2 may have a single bone fasteners hole, threebone fastener holes or any number of bone fastener holes.

FIG. 2 a illustrates an exemplary fastener 40 for use in fixing theplate 1 to the targeted vertebral bodies. The illustrated fastener 40 isa bone screw having a head portion 46 and a threaded shank portion 56.The head portion 46 may have a drive recess 58 configured to receive adriving tool, and a circumferential groove 44 configured to receive aportion of the previously-described retention clip 38. The head portion46 may have an angled underside 60 configured to facilitate expansion ofthe retention clip 38 when the fastener is inserted into the associatedbone fastener hole 6, 8 and driven into bone. When the fastener head 46passes far enough through the hole, the clip 38 snaps back into thegroove in the head 46, thus capturing the screw head within the hole 6,8.

Further details and embodiments of appropriate fasteners, retentionclips and bone fastener hole designs may be found in co-pending U.S.non-provisional patent application Ser. No. 10/653,164 entitled “BonePlate with Captive Clips”, by Duong, et al., filed Sep. 3, 2003, theentire contents of which are incorporated by reference. It should bepointed out that while bone fastener holes 6, 8 have been described andillustrated as having a clip 38 to resist fastener back out, any numberof well-known fastener holes and fasteners may be employed with boneplate 1, including bone fastener holes that are relatively smooth,partially or fully threaded, straight or conically shaped, elongatedslots, with or without ramped surfaces to provide compression orcombination holes that are both threaded and contain smooth rampedsurfaces.

FIG. 3 a shows a plate 61 that may be used in a two-level fusionprocedure, and may have a fixed plate portion 62 with first and secondends 64, 66, and first and second bone fastener holes 68 a, 68 bdisposed therebetween. The bone fastener holes 68 a, 68 b may beconfigured to receive fasteners to fix the plate portion 62 to a firstvertebral body. The fixed plate portion 62 may have a longitudinal axisB-B and each of the first and second ends 64, 66 may have a carriageblock engaging portion 70, 72. First and second carriage blocks 74, 76may slidingly engage the carriage block engaging portions 70, 72 of thefixed plate portion 62 to allow the carriage blocks 74, 76 to translatewith respect to the fixed plate portion 62 along the plate axis B-B. Thefirst and second carriage blocks 74, 76 may each have bone fastenerholes 78 a, 78 b; 80 a, 80 b configured to receive fasteners 40 to fixthe carriage blocks to respective vertebral bodies positioned onopposite sides of the first vertebral body.

The carriage blocks 74, 76 and the respective carriage block engagingportions 70, 72 of the fixed plate portion 62 may have translationsurfaces and compression and extension stop surfaces as described abovein relation to the plate segment 2 and carriage block 4 of FIGS. 1 a and1 b. These translation and stop surfaces may allow the carriage blocks74, 76 to move along the longitudinal axis B-B of the fixed plateportion 62, within a predetermined range of linear translation. Thus,the translation and stop surfaces may allow the carriage blocks 74, 76to move from a fully extended configuration (see FIG. 3 a) in which theplate has a length “PL₁” of from about 20 mm to about 100 mm, to a fullycompressed configuration (see FIG. 3 b) in which the plate has a length“PL₂” of from about 16 mm to about 96 mm. The carriage blocks and fixedplate portion preferably may be configured provide up to 12 mm ofcompression between adjacent vertebrae to accommodate post-operativesettling of the intervertebral spacer between the vertebral bodies. Eachcarriage block 74, 76 may individually move up to 6 mm with respect tothe fixed plate 62.

The plate 61 may be curved to generally conform to the curvature of theportion of the spine to which it will be attached. In addition, thesurgeon may wish to customize the plate to further conform to thespecific anatomy of the individual patient. Thus, as illustrated in FIG.3 a, the fixed plate portion 62 may be provided with one or more bendingnotches 63 a, 63 b disposed a predetermined distance “ND” away from thetranslating surfaces to provide a safe location for plate bending, thusensuring that such bending will take place in the plate portion 62, thatdoes not contain the carriage blocks 74, 76, and thus not compromise thesliding interaction between the carriages 74, 76 and the plate portion62. These notches 63 a, 63 b may be configured to be easily engaged witha standard bending tool. Notches may additionally be formed in the lowersurface of plate 62, preferably opposite notches 63 a, 63 b on the topsurface.

The plate 61 of FIGS. 3 a-3 b may have at least one recess 82 configuredto receive a drill guide or other tool for pre-forming a hole in thevertebral body into which the bone screws will be inserted to fix theplate 61 to the vertebrae. In the illustrated embodiment, and as shownin detail in FIG. 3 c, the recess 82 comprises a dog-bone shape having apair of threaded holes 84 a, 84 b disposed at each end of a slot 86. Thethreaded holes 84 a, 84 b may each have a midpoint 87 a, 87 b, with adistance “MPD” between the midpoints. The distance MPD may be at leastabout 1 mm. The threaded holes may engage a threaded or otherwiseengageable portion of a drill guide, such as those described, interalia, in co-pending U.S. patent application Ser. Nos. 10/619,472 toRathbun, et al., filed Jul. 16, 2003 and titled “Plating System withMultifunction Drill Guides,” and Ser. No. 10/639,515 to Binder Jr. etal., filed Aug. 13, 2003 and titled “Quick-Release Drill-guide Assemblyfor Bone Plates”, the entire contents of each application areincorporated herein.

In an alternative embodiment, the recess 82 at least partially comprisesa polygonal shape, such as a hexagon, rectangle, or square. The recess82 may also take the shape of a plurality of polygonal shapes, forexample, two overlapping hexagons may comprise the shape of the recess82 to form a combination-polygonal recess. These embodiments may beparticularly useful in single-assembly plates with a reduced area inwhich to place a recess 82 for purposes of aligning a drill guide orsimilar instrumentation. An embodiment of a hexagon-shaped recess 82 isshown in FIG. 3 d. While an embodiment of a square-shaped recess 82 isshown in FIG. 3 e. An embodiment of a translational plate assemblyutilizing an overlapping hexagon-shaped recess 82 is shown in FIG. 3 f.The recess 82 may also serve a spacer-visualization function, allowingthe surgeon to view the position of the intervertebral spacer after theplate 61 has been installed.

A second recess 88 may be provided adjacent recess 82 and may beconfigured to receive a temporary attachment pin (not shown) totemporarily fix the plate 61 to at least one vertebral body whilefastener holes are being drilled in the bone. The pin may have asharpened tip to allow easy penetration into the bone cortex, and thetip may also have threads configured to affirmatively engage the bone.

Alternatively, recess 82 may serve both the function of engaging theengageable portion of a drill guide and receiving an attachment pin, asdescribed above. A polygonal or combination-polygonal recess 82 may beespecially useful for these purposes, with the attachment pin being ofthe appropriate shape and size to fit snugly within at least a portionof the recess 82 and into an appropriately shaped hole in a separateplate.

Moreover, a motion-limiting shim 85 as shown in FIGS. 3 d-3 f, may beinserted into the recess 82, for limiting the translation of at leastone plate unit during use. At least a portion of shim 85 may be shapedto fit in at least a portion of the recess 82 so that the shim 85 willnot translate in the recess. Based on the shape of the recess 82, theshim 85 may be of a corresponding shape, similar to the attachment pindescribed above. At least a portion of the shim 85 extends down andblocks the pathway in which the carriage block moves. The recess 82 maybe configured in that the shim 85 may be inserted at multiple locationsso a user can adjust the amount of distance the carriage block maytravel before the shim 85 would prevent further movement. The shim 85being inserted into the top of the bone plate may be easily used andimplemented during the implant procedure since the top of the plateshould be readily accessible. The portion of the shim 85 that contactsthe carriage block may include a cantilevered section or leaf springthat will provide increased resistance to the movement of the carriageblock as the carriage block translates until it has moved apredetermined distance at which point the shim 85 may prevent anyfurther movement of the carriage block. At least a portion of a shim 85should also be accessible to a user, so that the shim may be removable.An alternative embodiment of a motion-limiting shim is discussed infrain FIG. 9, along with greater detail of motion-limiting shims generally.The recess 82 and 88 as well as the motion-limiting shim 85 described inreference to plate 61 and shown in FIGS. 3 c-3 f, optionally may eachindividually or in combination be incorporated into the bone plate 1described supra.

FIG. 4 a shows a plate 101 for use in a three level fusion procedure.The plate 101 may have a fixed plate portion 106 with first and secondends 108, 110 each having a carriage block engaging portion 112, 114,and a longitudinal axis C-C. The fixed plate portion 106 may have twopairs of bone fastener holes 116 a, 116 b; 118 a, 118 b for engaging apair of adjacent vertebrae. The first pair of bone fastener holes 116 a,116 b may be round and thus may be used to rigidly fix the plate portionto the underlying vertebral body. The second pair of bone screw holes118 a, 118 b may be slotted, with each hole having a slot axis “SA-SA”oriented substantially parallel to the plate axis C-C. The slotted holes118 a, 118 b may have a slot length “SL” as measured from the centroid“X,” “Y” of the circles that bound the ends of the holes 118 a, 118 b.The slot length “SL” may be from about 0.5 mm to about 10 mm.

The slotted holes 118 a, 118 b may be configured to allow the head 46 ofan associated bone screw to translate along the slot axis SA duringoperation. This may allow the adjacent vertebral bodies to translatewith respect to each other along the plate axis C-C after the plate 101has been attached to the vertebra using bone fasteners 40 insertedthrough the round and slotted bone fastener holes 116 a, 116 b; 118 a,118 b. Thus, the slot length SL may be dimensioned to allow apredetermined amount of translation between the vertebral bodies duringoperation. The slot length SL as measured between the respectivecentroids X, Y of the circles that define the slot ends 119 a, 119 b maybe from about 0.5 mm to about 10 mm.

As shown in detail in FIG. 4 b, the slotted holes 118 a, 118 b may haveall the features as previously described in relation to the round holesof FIG. 1 c, including appropriate features for receiving a retentionclip 38 (see FIG. 2 b) for securing a bone fastener 40 within theslotted hole 118 a, 118 b during use. Where retention clips 38 are used,the arms 48, 50 of the clips 38 may have a length “CL” sufficient toengage the groove 44 in fastener head 46 at any point along the lengthSL of the slotted hole 118 a, 118 b. Thus, the retention clip 38 mayhave a length CL that is greater than that of clips used in the roundbone screw holes 116 a, 116 b.

The plate 101 of FIG. 4 a may further have first and second carriageblocks 120, 122 engaged with respective first and second ends 108, 110of the fixed plate portion 106 to allow the plate 101 to engage thirdand fourth vertebral bodies. The carriage blocks 120, 122 may have allof the features of the carriage blocks described above in relation toFIGS. 1 a-1 g and 3 a-3 f. Thus, each carriage block 120, 122 may haveat least one bone fastener hole 124 a, 124 b; 126 a, 126 b for engagingan underlying vertebral body, and may have translating surfaces asdescribed above in relation to FIGS. 1 a-1 g and 3 a-3 f to allow thecarriage blocks 120, 122 to translate with respect to the fixed plateportion 106 along the plate axis C-C within a predetermined amount, alsoas previously described.

FIG. 5 a shows a plate 128 for use in a three-level fusion procedure.The plate 128 may have a fixed plate portion 130 with first and secondends 132, 134 each having a carriage block engaging portion 136, 138,and a longitudinal axis D-D. The fixed plate portion 130 may have onepair of round bone screw holes 140 a, 140 b for rigidly fixing the plateportion 130 to an underlying vertebral body. The plate 128 may furtherhave first and second end carriage blocks 142, 144 engaged withrespective first and second ends 132, 134 of the fixed plate portion 130to allow the plate 128 to translatably engage second and third vertebralbodies. The end carriage blocks 142, 144 may have any or all of thefeatures of the carriage blocks described above in relation to theprevious figures, and thus, each carriage block 142, 144 may have atleast one bone fastener hole 146 a, 146 b; 148 a, 148 b for engaging anunderlying vertebral body, and may have appropriate translating surfacesconfigured to cooperate with the first and second ends 132, 134 of theplate to allow the carriage blocks 142, 144 to translate with respect tothe fixed plate portion 130 along the plate axis D-D within apredetermined range as previously described.

The plate of FIG. 5 a may also have an internal carriage block 150disposed between the bone screw holes 140 a, 140 b and end carriageblock 144 to allow the plate to translatably engage a fourth vertebralbody. As shown in greater detail in FIG. 5 b, the internal carriageblock 150 may have upper and lower surfaces 152, 154 and a fastener hole156 in communication therewith. The internal carriage block 150 mayfurther have a pair of side surfaces 158 a, 158 b; 160 a, 160 bconfigured to slidingly engage corresponding side surfaces 162 a, 162 b;164 a, 164 b of a longitudinal recess 166 formed in the fixed plateportion 130. In one embodiment, the side surfaces 158 a, 158 b; 160 a,160 b of the internal carriage block 150 may be “v”-shaped and maycorrespond to inverted “v”-shaped side surfaces of the recess 166. The“v”-shaped arrangement of side surfaces 158 a, 158 b; 160 a, 160 b maytraverse about 90% of the thickness “BT” of the carriage block, whichmay impart a degree of lateral flexibility to the carriage block toallow it to be laterally compressed to “snap” it into the recess 166,which may therefore facilitate the insertion of the carriage block 150into a recess 166. The carriage block 150 may be retained within therecess by the interaction of the corresponding side surfaces 158, 162;160, 164. The carriage block 150 may further have compression andextension stop surfaces 168, 170 configured to engage correspondingsurfaces 172, 174 of the recess 166. The internal carriage block 150 mayhave a length “ICL” and the recess 166 may have a length “IRL.” Ingeneral, the length IRL will be greater than the length ICL to allow athe internal carriage block 150 to slide within the recess 166.

The internal carriage block 150 may slide within the recess 166 alongthe longitudinal axis of the plate “D-D” between the respectiveextension and compression stop surfaces 174, 172 of the plate 130.Length ICL may be from about 5 mm to about 20 mm, while length IRL maybe from about 7 mm to about 30 mm. As noted, the lengths will beselected to provide a desired amount of translation “TL” between thecarriage block and the fixed plate portion to thus accommodate a desiredtranslation between the vertebrae attached to the fixed plate portion130 and the internal carriage block 150. The translation may preferablybe from about 5 mm to about 25 mm.

It is noted that although the illustrated embodiment comprisescorresponding “v”-shaped surfaces, the side surfaces of the screwcarriage and slot may assume any shape appropriate to allow the desiredlongitudinal sliding while preferably preventing the carriage fromdisengaging from the slot. Thus, dovetail surfaces, “u”-shaped surfaces,mortise-and-tenon surfaces, channels, grooves, ridges, etc. may also beused as desired.

The fastener hole 156 of the internal carriage block 150 may have allthe features as previously described in relation to the round holes ofFIG. 1 c, or the slotted holes of FIGS. 4 a-4 b, including appropriateconfigurations for receiving a retention clip 38 (see FIG. 2 b) tosecure a bone fastener 44 (see FIG. 2 a) within the hole 156 during use.

FIG. 5 c shows a two-piece internal carriage block 178 that may be usedwith the plate 128 of FIG. 5 a. The two-piece carriage block 178 may bedivided substantially into halves 180 a, 180 b along the blocklongitudinal axis “E-E.” The block halves 180 a, 180 b may bedisassembled, shifted longitudinally with respect to each other, nestedtogether, and installed within the plate recess 166 in the nested state.Once they have been installed in the recess 166, the halves 180 a, 180 bmay be realigned and fit back together to form a unitary piece. Theretention clip 38 may then be installed within the appropriate groove182 a, 182 b in the block halves 180 a, 180 b and may function tomaintain the halves together during operation. This configurationeliminates the need to provide a “flexible” internal carriage block withindents 176 a, 176 b, and may provide a carriage block that is easier tomachine and assemble.

The plate 184 of FIG. 6 may be used in a four-level fusion procedure andmay have a plate portion 186, first, second and third internal carriageblocks 188, 190, 192 and first and second ends 194, 196 for engaging apair of end carriage blocks 198, 200 in a manner similar to thatdescribed in relation to the plate of FIG. 5 a. The plate portion 186may have a longitudinal axis F-F, and may have first, second and thirdintermediate recesses 202, 204, 206 disposed along the axis F-F forcooperating with the first, second and third internal carriage blocks188, 190, 192, respectively. It is noted that while the plate 184 isshown for use in a four-level fusion procedure, it could easily beconfigured for use in a three or two-level procedure simply byshortening the plate and providing fewer internal carriage blocks.Likewise, the plate portion 186 could be provided with one or more setsof holes, preferably slotted holes, in lieu of one or more of theinternal carriage blocks.

In addition, the internal carriage blocks 188, 190, 192 may have any orall of the features described in relation to the plate 128 of FIG. 5 a,and the end carriage blocks 198, 200 may have any or all of the featuresdescribed in relation to FIGS. 1 a-5 c.

The plate 208 of FIG. 7 a combines some of the features of thepreviously described plates into a single plate for use in a four-levelspinal fusion procedure. The plate 208 may have a fixed plate portion210 with first and second ends 212, 214, one pair of round holes 216 a,216 b for engaging a first vertebra, one pair of slotted holes 218 a,218 b for engaging a second vertebra, one internal carriage block 220disposed in recess 222 for engaging a third vertebra, and a pair of endcarriage blocks 224, 226, each configured to engage a respective end212, 214 of the fixed plate portion 210. Thus configured, the plate 208may be rigidly fixed to the first vertebra, while the remainingvertebrae may translate with respect to the first vertebra via theslotted holes 218 a, 218 b, internal carriage block 220, and endcarriage blocks 224, 226 as previously described. Moreover, all of thebone fastener holes may be configured similarly to that described inrelation to FIGS. 1 c and/or 4 a-4 b, and may have retaining clips 38configured to retain a bone screw 44 therein.

FIGS. 7 b-7 c show a similar single plate for use in a four-level spinalfusion procedure, but without an internal carriage block 220. Instead,the embodiments of FIGS. 7 b-7 c have two pairs of slotted holes 218 a,218 b and 218 c, 218 d.

FIG. 8 a shows a plate 228 for use in a two-level fusion procedure, theplate having a two-piece sandwich style plate portion 230 comprising atrack base 1000 and top plate 2000. The plate portion 230 engages threecarriage blocks 300 a, 300 b, 300 c via respective recesses 1116 a, 1116b, 1116 c formed in the track base 1000.

The carriage blocks 300 a, 300 b, 300 c each may include one or morefastener holes 340 a, 340 b, 340 c configured to receive fasteners 44 tofix the carriage blocks to associated vertebrae. The track base 1000 mayhave first and second ends 1020, 1040 and may have a curved profile toallow the plate 228 to more closely match the contour of the patient'sspine. The top plate 2000 may likewise have first and second ends 2020,2040 and may have a curved profile that substantially matches that ofthe track base.

The top plate 2000 may have a pair of lateral alignment flanges 1022,1024 and at least one bore 2060 for receiving a holding fastener 400 forsecuring the top plate 2000 to the track base 1000. Any appropriatefastening means may be provided to fix the top plate to the track base,including but not limited to screws, rivets, press-fit, laser welding,brazing, or suitable adhesives. The alignment flanges 1022, 1024 mayserve to align the top plate and track base, and to provide the plate228 with increased strength in bending and torsion.

The top plate 2000 and track base 1000 may be assembled so as to retainthe carriage blocks 300 a, 300 b, 300 c within associated recesses 1116a, 1116 b, 1116 c so that the carriage blocks may slide within therecesses, thus providing the desired translation capability between theengaged vertebrae. The carriage blocks engage the respective recessesvia reduced-size central portions 1350 a, 1350 b, 1350 c.

Two-hole carriage blocks 300 a, 300 b, 300 c may be provided, and aspreviously described in relation to the plate of FIG. 1 a, the carriageblock fastener holes 340 a, 340 b, 340 c, may be configured to receiveretention clips 38 (see FIG. 2 b) for retaining the bone fasteners 44(see FIG. 2 a) in the holes during operation. FIG. 8 b shows the plateof FIG. 8 a in the assembled position.

FIGS. 8 c-8 f show carriage block 300 in greater detail. As illustratedin FIGS. 8 c and 8 d, carriage block 300 may comprise a pair offastening portions 370 a, 370 b and a connecting portion 350 disposedtherebetween. The connecting portion 350 may have first and second ends392 a, 392 b, which may be configured to conform to correspondingoutside and inside walls 1117 a, 1117 b of an associated plate recess1116 a, 1116 b, 1116 c into which the carriage block 300 will fit. Inthe illustrated embodiment, connection portion 350 has a concave firstend 392 a to engage a correspondingly curved recess end (outside wall1117 a or inside wall 1117 b, see FIG. 8 a).

The carriage block 300 of FIGS. 8 e and 8 f have fastener holes 340 thatmay be offset longitudinally from the center of the connecting portion35 by a length OL. This offset ensures that in use, the outer edges 390a, 390 b of the carriage block 30 will not extend beyond the ends 2020,2040 of the top plate 2000, even where the plate and carriage blocks arein the fully compressed configuration. Such an arrangement provides theadvantage that it prevents any portion of the top plate 2000 fromprotruding either into or undesirably close to the adjacent disc spacewhen the carriage blocks translate fully within their associatedrecesses.

The carriage block 300 may have compression and extension surfaces 392a, 392 b configured to engage corresponding surfaces 1117 a, 1117 b ofthe associated recess 1116 formed in track base 1000. Thus configured,the connecting portions 350 of the carriage blocks 300 a, 300 b, 300 cmay be received within the corresponding recesses 1116 a, 1116 b, 1116 cin the track base 1000 and may translate along the plate to provide thedesired translation of adjacent vertebral bodies.

FIG. 8 g shows an alternative carriage block 90 having three fastenerholes 92 a, 92 b, 92 c, that may be used with a plate such as the plate61 shown in FIG. 3 a. Fastener hole 92 c may be offset from fastenerholes 92 a, 92 b and may be disposed substantially along thelongitudinal axis B-B of the plate 61. The additional fastener hole 92 cmay increase the retention of the plate with the associated vertebralbody. This may be particularly advantageous where the plate is subjectedto significant forces and moments in use which may tend to pull thefastener out of engagement with the bone.

The plate engaging portion 94 of the three-hole carriage block 90 may beslidably received within a plate, such as the carriage block-engagingportions 70, 72 of the plate 61 as previously described in relation tocarriage blocks 74, 76. The plate engaging portion 94 may also compriseextension and compression stop surfaces 96, 98 similar to thosedescribed in relation to blocks 74, 76 to limit the total movement ofthe carriage block 90 along axis B-B with respect to the fixed plateportion 61. The extension and compression ranges of movement andresistance to movement may be the same as for the previously describedcarriage blocks.

In order provide the surgeon the option to limit or prevent pre- orpost-implantation translation of any or all of the carriage blocksdescribed herein (such as elements 4, 74, 76, and 300) for use with anyplate or plate element described herein, a motion limiting shim 500,shown in FIG. 9, may be provided. Shim may be positioned between thecarriage block 300 and one of the sides 1117 a, 1117 b of the associatedrecess 1116 a, 1116 b, 1116 c. Such an arrangement may allow the surgeonto customize the amount and direction of translation of one or more ofthe carriage blocks. The shim 500 may be made of a flexible material,such as elgiloy or nitinol, or may be made of a suitable bioresorbablematerial. Shim 500 is preferably composed of a biocompatible material.As illustrated in FIG. 9, the shim 500 may have opposing flexible tabs520 a, 520 b that may allow an operator to compress the shim to positionit within the targeted recess 1116. In particular, flexible tab 520 amay be actuated by applying pressure to bulbous tab 560. Shim 500 mayhave a height “SH” that may be the maximum distance a shim may occupyalong the longitudinal axis of a plate. Moreover, shim 500 may havegripping tabs 522 a, 522 b that may allow an surgeon to grip the shim500 to move it to a desired location within a plate, or remove itcompletely from a plate. Side surfaces 524 a, 524 b may correspond tothe outer edges of a flange 1022 (see infra FIG. 10), or may generallycorrespond to a translating surface of a carriage block and/or platesegment, depending at least in part how shim 500 is situated in relationto a carriage block and/or plate segment.

FIG. 10 illustrates a plate having a cam-compression feature for usewith any of the previously described plates. This feature is operable toallow the surgeon to adjust the recess length to minimize or preventtranslation of the associated carriage block, or to induce a compressionforce between adjacent vertebrae to aid in seating a spinal fusionimplant inserted therebetween.

The cam 1140 may be elliptical, with an arcuate camming surface 1142configured to correspond to an arcuate surface 392 on the connectingportion 350 of the associated carriage block 300 (see, e.g., FIG. 8 c).The cam 1140 may have an unactuated position in which the cam majordiameter is oriented substantially perpendicular to the longitudinalaxis of the plate, and an actuated position in which the cam majordiameter is oriented substantially parallel with respect to thelongitudinal axis of the plate. The unactuated cam position maycorrespond to a maximum recess length S_(M), while the actuated positionmay correspond to a minimum recess length S2.

Thus, prior to fixing the carriage blocks to the adjacent vertebrae, thecam 1140 may be rotated sufficiently to shift the adjacent carriageblock 300 in a first direction toward the one of the walls 1117 b of therecess 1116, thus minimizing or eliminating the gap between the insidewall and the connecting portion 350 of the carriage block 300. Once thecam 1140 position is set, the carriage blocks 300 may then be fixed tothe adjacent vertebrae to provide a translation plate having, ifdesired, a reduced translation length for each carriage block 300. Thisprovides the benefit of allowing the surgeon to easily adjust the amountof translation desired for each level of fixation to suit the anatomyand physiology of the individual patient.

The cam 1140 may also be used to induce a compression force betweenadjacent vertebrae to aid in seating a spinal fusion implant insertedtherebetween. Thus, first and second carriage blocks 300 a, 300 b may befixed to adjacent vertebrae with the cam 1140 in the unactuatedposition. Thereafter, the cam 1140 may be rotated to the actuatedposition, which may shift the first carriage block 300 a toward thesecond carriage block 300 b. This movement may cause the underlyingvertebra to move with the first carriage block 300 a toward the secondcarriage block 300 b, thus reducing the space between the vertebrae andapplying a compressive force between the vertebral end plates and aspinal fusion spacer placed therebetween.

As can be seen in FIG. 10, dashed line “DL” shows the expected positionof the carriage block 300 after a single 90-degree rotation of the cam1140. To achieve this expected position, carriage block 300 would move alongitudinal distance S1 toward the center flange 1022. Further rotationof the cam 140 would move the carriage block 30 a second distance S2,until the second end 390B of the carriage block 300 abuts the centerflange 1022 of the top plate 20.

The cam 1140 may be secured to the track base 1000 with a holdingfastener 400 or any other appropriate fastening method. In oneembodiment, the fastener may serve both to secure the cam 1140 to thetrack base 1000 and to provide a means of actuating the cam. Thus, thefastener 400 may have a recess suitable for receiving a driving and/oradjusting tool.

FIG. 11 shows a plate 232 for use in a corpectomy procedure, in which atleast a portion of at least one vertebral element is removed. Thus, theplate 232 spans the space left by the removed element or elements. Plate232 may have a plate portion 234 with first and second ends 236configured to cooperate with a pair of end carriage blocks 238, 240. Inthe illustrated embodiment, end carriage block 238 has a third platehole as previously described in relation to FIG. 8 g. Plate 232 furthercomprises a pair of elongated viewing windows 242, 244 suitable to allowthe surgeon to visualize a corpectomy graft placed between the affectedvertebrae. The plate 232 of FIG. 11 may further incorporate any or allof the features previously described in relation to the embodiments ofFIGS. 1 a-10 (e.g., plate and carriage block curvatures, straight andoffset carriage blocks, shim arrangements, cam features, fastenerlocking clips, etc.)

FIGS. 12 a and 12 b show a plate 900 that may be provided in twoextensible pieces 901, 908, which may allow the plate itself to bear aportion of the translation. This extensible two-piece design also mayallow the surgeon to adjust the length of the plate to fit the anatomyof a particular patient. Thus first extensible piece 901 may have afirst end 903 engaged to a first carriage block assembly 300 a, and asecond end 905 configured to be telescopically received within a firstend 907 of the second extensible piece 908. Likewise, the secondextensible piece 908 may have a first end 907 configured for telescopicengagement with the first piece 901 and a second end 909 engaged to asecond carriage block assembly 300 b. The second extensible piece 908may have a locking device 906, which may lock the relative positions ofthe first and second pieces. In the illustrated embodiment, the lockingdevice 906 is an elliptical cam associated with both the first andsecond plate portions 901, 908. The cam 906 may have a major diametersubstantially aligned with the longitudinal axis K-K of the plate 900when in the unlocked position, such that rotating the cam 906 slightlymay configure it to the locked position, thereby fixing the pieces 901,908 together. After adjustment of first extension piece 901 and secondextension piece 908, the pieces may be fixed together so that they willnot move relative to each other upon implantation in the spine. Thus, itis intended that upon implantation, first extension piece 901 will notmove relative to second extension piece 908 in situ. Meanwhile, carriageblocks 300 a, 300 b would provide for in situ movement relative to thefirst and second extension pieces 901, 908, and to each other. uponimplantation of the plate 900. FIG. 12 a shows plate 900 in a closed orcompressed position, while FIG. 12 b shows the plate 900 in an open orextended position. As with the previous embodiments, the plate of thisembodiment may comprise any or all of the applicable plate and carriageblock features described in relation to all previous embodiments.Further, the plate of this embodiment may be used for single ormultiple-level corpectomy or fusion procedures or combinations thereof.

FIGS. 13 a and 13 b show another embodiment of a fixation assembly 600including a plate 602 with dovetail portions 612 configured to receiveat least a portion of a carriage block 604. In this embodiment, carriageblock 604 is allowed to initially engage a dovetail portion 612, andthereafter the end 622 of the dovetail portion 612 is deformed at ornear the end 617 of the carriage block 604 to effectively limit themotion of the carriage block and prevent it from disengaging with theplate 602. End 622 may be deformed by any suitable method, includingswaging.

Plate 602 may have fastener holes 606 a, 606 b, 608 a, 608 b, 610 a, 610b, which may be circular or slot-shaped. Moreover, plate 602 may includeany or all of the characteristics of previously described plates,including clips, recesses, internal carriage blocks, etc.

Carriage block 604 may translate along dovetail portion 612 in use,which may be limited by the deformed end 622 in one direction, and astop surface 614 in another direction. As described in more detailabove, carriage block 604 may translate in situ, with or withoutfasteners 660 inserted into fastener hole 616 a, 616 b, which mayprovide locations for inserting fasteners 660 into a bone segment.

As shown in detail in FIG. 13 b, carriage block 604 may have translationsurfaces 618, and plate 602 may have translation surfaces 620. Asdescribed in more detail above, as carriage block 604 translates withrespect to plate 602, translation surfaces 618, 620 may slidinglyengage, and may create a variable amount of friction along the length ofthe dovetail portion 612. As with plate 602, carriage block 604 mayinclude any or all of the characteristics of carriage blocks describedabove.

Dovetail portion 612 may have a variety of shapes and sizes, based inpart on the desired strength of the assembly 600. For instance, it maybe beneficial to have a wider, and overall larger, dovetail portion 612where the expected in situ forces on the assembly 600 are expected to besubstantial.

FIGS. 14 a-14 b are perspective views of yet another embodiment of afixation assembly 700 having a plate 702 and carriage blocks 704 a, 704b. Plate 702 may have a window 707 for increased visualization, and atleast one fixation hole 710 with at least one drill guide key 711disposed adjacent to the fixation hole 710. Similarly, carriage blocks704 a, 704 b may also have fixation holes 713 and drill guide keys 714.Drill guide keys 711, 714 may receive at least a portion of a drillguide (not shown), and may assist in aligning a drill barrel (not shown)with a fixation hole.

In this embodiment, plate 702 has ends 703, and may engage carriageblocks 704 a, 704 b at tapered engaging surfaces 706 a, 706 b,respectively. Ends 703 of plate 702 may be shaped and/or formed suchthat carriage blocks 704 a, 704 b are prevented from sliding off theplate 702. As seen in FIG. 14 a, carriage blocks 704 a, 704 b are in acompressed condition, whereby the assembly 700 may be in its shortestconfiguration along its longitudinal axis. FIG. 14 b shows the assembly700 in an expanded condition, whereby carriage blocks 704 a, 704 b eachhave translated along tapered engaging surfaces 706 a, 706 b,respectively, and in the direction of the adjacent arrows. In thisconfiguration, the overall length of assembly 700 may be greater alongthe longitudinal axis, as compared to the configuration shown in FIG. 14a.

The tapered engaging surface 706 b is shown in more detail in FIG. 15.As seen in this embodiment, tapered engaging surface 706 b has sidetapered surfaces 708 a, 708 b, with a substantially flat surface 709disposed therebetween. Side tapered surfaces 708 a, 708 b may beprogressively tapered, such that the resistance between a carriage block704 b and the tapered engage surface 706 b increases as the carriageblock 704 b (not shown, for clarity) attempts to translate toward thecenter of plate 702. The result of such an arrangement may be that itrequires more force to compress assembly 700, than is required tolengthen assembly 700. As further seen in FIG. 15, plate 702 may alsohave stops 716, which may limit the movement of carriage block 704 brelative to the plate 702.

An embodiment of a carriage block 704 is shown in FIG. 16, whereincarriage block 704 may have fixation holes 713 and drill guide keys 714,as also shown in FIGS. 14 a-15. As also seen in this embodiment,carriage block 704 may have a contoured opening 720 having taperedsurfaces 721, 722 for engaging a tapered engaging surface 706 of plate702, and disposed between lobes 725. Carriage block 704 may engage atapered engaging surface 706 of plate 702 in such a way that as carriageblock 704 is urged toward the center of plate 702 (i.e. toward a morecompressed condition), carriage block 704 flexes such that lobes 725 arepushed upward by the tapered engaging surface 706 of plate 702. If thetapered engaging surface 706 is contoured to provide progressiveresistance, the carriage block 704 may experience greater flexure as itis progressively urged closer to the center of plate 702. As such,carriage block 704 may be constructed of a resilient material which mayflex back upon the movement of the carriage block 704 away from thecenter of the plate 702 and toward the end 703 of plate 702 (i.e. towarda more expanded condition).

Progressive resistance of a tapered engaging surface 706 may be achievedby increasing the angle of tapered side surfaces 708 a, 708 b along thelongitudinal axis of plate 702. Progressive resistance may also beachieved by surface roughening. Other methods will be appreciated bythose skilled in the art.

Another embodiment of a fixation assembly 800 is shown in FIGS. 17 a-17b. In this embodiment, plate 802 may have a plurality of windows 807,and two sets of fixation holes 810 a, 810 b, wherein fixation holes 810a may be substantially slot-shaped, and fixation holes 810 b may besubstantially circular. Fasteners 830 may be configured to translatewithin slot-shaped holes 810 a. Plate 802 may also have ends 803, andtapered engaging surfaces 806 with carriage blocks 804 a, 804 b disposedthereon. Carriage blocks 804 a, 804 b may again have fixation holes 813for receiving a fastener 830. Plate 802 and carriage blocks 804 a, 804 bmay also each have drill guide keys 811, 814 for the same purposes asdiscussed above in relation to FIGS. 14 a-14 b. Fastener 830 may be ascrew.

Assembly 800 may also initially have tabs 825 a, 825 b disposed betweencarriage blocks 804 a, 804 b and plate 802. In use, tabs 825 a, 825 bmay serve to space carriage blocks 804 a, 804 b toward ends 803, whichmay configure assembly 800 in an expanded condition. This may beadvantageous for implantation purposes, as it may be beneficial toinstall assembly 800 into a patient with the assembly 800 in an expandedcondition. Tabs 825 a, 825 b are shown to be removed in FIG. 17 b. Inthis embodiment, carriage block 804 b has translated completed towardthe center of the plate 802, in the direction of the adjacent arrow. Incontrast, carriage block 804 a has not translated, revealing a portionof the tapered engaging surface 806 a and stops 816 of plate 802. Assuch, the embodiment of FIG. 17 b is in a partially expanded (orpartially compressed) condition. In use, a surgeon preferably willremove tabs 825 a, 825 b after implanting assembly 800 in a patient.Tabs 825 a, 825 b may be disposable.

It is expressly contemplated that progressive resistance may be utilizedwith all embodiments as shown herein, as will be appreciated by those ofskill in the art. Moreover, it is contemplated that the components andfeatures of one embodiment may be combined and/or substituted forsimilar components in another embodiment. Lastly, progressive resistancemay be provided in any suitable direction and/or pattern. For instance,a tapered engaging surface 706, 806 may be tapered such that progressiveresistance is provided as a carriage block 704, 804 translates towardthe end 703, 803 of the plate 702, 802, instead of toward the center ofthe plate 702, 802.

It should be noted that the aforementioned descriptions andillustrations have been provided as examples of the configurations oftranslation plates that may be designed and assembled using theprinciples of the invention. These examples will be understood to one ofordinary skill in the art as being non-limiting in that a translatingplate employing one or more of the disclosed features may be produced asdesired or required for a particular patient's need. Thus, the featuresdisclosed are “modular” in nature.

For example, the plate itself may be provided in either the one-piecedesign of FIGS. 1 a-7 c, or the two piece design having a top plate andtrack base of FIGS. 8 a-8 b. The one or two piece plate designs also maybe provided with integral screw holes (FIGS. 1 a-7 c) to allow the plateelement itself to be screwed to an underlying vertebra, or they may nothave integral screws holes (FIGS. 8 a-8 g and 10-12 b) such that theplate itself engages the underlying vertebrae only via the carriageblocks.

Furthermore, the one or two piece plates may employ any combination ofcarriage block designs desired (e.g. offset type (FIGS. 8 e-8 f),non-offset type (FIGS. 8 c-8 d), third-hole type (FIG. 8 g) or internaltype (FIGS. 5 a-5 c, 6, 7 a)).

Each of the fasteners and fixation plates disclosed herein may be formedof a titanium alloy such as titanium-aluminum-niobium, which may beanodized. One material for use with each of the plates and screwsdescribed herein is Ti-6Al-7Nb, with a density of about 4.52 gm/cc, amodulus of elasticity of about 105 GPa, an ultimate tensile strength ofabout 900 MPa, and a yield strength of about 800 MPa. Surfaces of thefasteners may also be burr free, with all sharp edges having a radius toa maximum of about 0.1 mm. Further, the retention clips 38 may befabricated from titanium, titanium alloy, or elgiloy.

While the invention has been shown and described herein with referenceto particular embodiments, it is to be understood that the variousadditions, substitutions, or modifications of form, structure,arrangement, proportions, materials, and components and otherwise, usedin the practice and which are particularly adapted to specificenvironments and operative requirements, may be made to the describedembodiments without departing from the spirit and scope of the presentinvention. Accordingly, it should be understood that the embodimentsdisclosed herein are merely illustrative of the principles of theinvention. Various other modifications may be made by those skilled inthe art which will embody the principles of the invention and fallwithin the spirit and the scope thereof.

1. A fixation assembly comprising: a carriage block portion having atleast one fixation hole configured to receive a bone fastener; a baseportion that is elongate along a longitudinal direction, the baseportion having a top surface, a bottom surface, and a recess thatextends into the top surface so as to be defined by opposed sidewalls,the recess configured to receive the carriage block; a plate portionthat is elongate along the longitudinal direction, the plate portionhaving a top surface, a bottom surface, and at least one bore thatextends between said the top surface and the bottom surface, the plateportion configured to be aligned with the base portion along atransverse direction that is perpendicular to the longitudinal directionsuch that the bore is configured to receive a fastener to couple theplate portion to the base portion to thereby retain the carriage blockportion within the recess and at a location between the base portion andthe plate portion; and a shim portion that is configured to be receivedbetween the carriage block and one of the sidewalls; wherein the shimportion limits the translation of the carriage block portion within therecess relative to the base portion along the longitudinal direction. 2.The fixation assembly of claim 1 wherein the plate portion has one ormore flanges along its lower surface that align the top surface of thebase portion with the lower surface of the plate portion when the baseportion and plate portion are coupled.
 3. The fixation assembly of claim1 wherein a resilient clip is disposed within the fixation hole to allowthe bone fastener to angulate.
 4. The fixation assembly of claim 1wherein the carriage block portion comprises a pair of fixation holesand a connection portion between the pair of fixation holes.
 5. Thefixation assembly of claim 1 wherein the shim portion comprises nitinol.6. The fixation assembly of claim 1 wherein the shim portion is madefrom a bioresorbable material.
 7. The fixation assembly of claim 1wherein the shim portion has flexible tabs that are configured tocompress the shim portion to allow the shim portion to be receivedbetween the carriage block portion and the one of the sidewalls of therecess.
 8. The fixation assembly of claim 1, wherein the base portionincludes the opposed sidewalls.
 9. The fixation assembly of claim 1,further comprising a second carriage block portion having at least onefixation hole configured to receive a second bone fastener, wherein thebase portion further has a second recess that extends into the topsurface so as to be defined by opposed second sidewalls, the secondrecess configured to receive the second carriage block.
 10. The fixationassembly of claim 9, wherein the second recess is spaced apart from therecess along the longitudinal direction.
 11. The fixation assembly ofclaim 10, wherein the carriage block is moveable along the longitudinaldirection within the recess, and the second carriage block is moveablealong the longitudinal direction within the second recess.
 12. Thefixation assembly of claim 10, further comprising a second shim portionthat is configured to be received between the second carriage block andone of the second sidewalls of the second recess, wherein the secondshim portion limits the translation of the second carriage block withinthe second recess relative to the base portion along the longitudinaldirection.
 13. A fixation assembly comprising: a first plate segmentthat is elongate along a longitudinal direction, the first plate segmenthaving a first translating surface, at least one fixation hole, and afirst recess; a carriage block that is elongate along the longitudinaldirection, the carriage block having a second translating surface, atleast one fixation hole, and a second recess that is at least partiallyaligned with the first recess along a transverse direction that isperpendicular to the longitudinal direction, and a shim that isconfigured to be receivable within at least a portion of the firstrecess and the second recess; wherein the first translating surface andthe second translating surface interact to permit translation of thefirst plate segment and carriage block relative to each other along thelongitudinal direction and the shim is configured to engage the carriageblock to thereby limit said translation when the shim is received withinat least a portion of the first recess and the second recess.
 14. Thefixation assembly of claim 13 wherein the shim is substantiallypolygonal shaped.
 15. The fixation assembly of claim 14 wherein thefirst recess is substantially polygonal shaped.
 16. The fixationassembly of claim 15 wherein the second recess is substantiallypolygonal shaped.
 17. The fixation assembly of claim 13 wherein the shimfurther includes a spring that increases resistance when the first platesegment and carriage block are translated relative to each other alongthe longitudinal axis.
 18. The fixation assembly of claim 13 whereinshim further includes a cantilevered portion that increases resistancewhen the first plate segment and carriage block are translated relativeto each other along the longitudinal axis.
 19. The fixation assembly ofclaim 13 wherein the shim comprises nitinol.
 20. The fixation assemblyof claim 13 wherein the shim is made from a bioresorbable material.